Built a custom D8B external power supply

[RJH_MUSIC]

Ah ha. So yes, that is the only step I did not follow from Ralph's post, shorting the Mgnd and Dgnd. I figured I didn't need to because I was not mounting the power supplies in the desk but that could have been wrong.

[RJH_MUSIC]

Now for my next problem. On both of my D8b's that are actually functioning in my studio, (NOT REBUILT) I'm having lately a lot of noise coming out of one of them on the bus outs. I realize I have 24 stereo instruments plugged into the thing but even with most of the fader's downI'm getting an awful lot of noise transferred over to my mackie 32x8 bus. It almost sounds like a combination of 60 cycle hum mixed in with fan noise the fan noise the frequency is the same. What should I look at replacing now?

[Bruce Graham]

HI RJH_Music;
This sound like a ground loop. Causes could be many things.
Is this a change from what was there before?
Is the power to all you gear on a UPS, or at least coming from the exact same power source?
Have you tried removing one output at a time to see if it is acumulative or to see if it is coming from a single source?
Are you Pin 1 lifted at the outputs and grounded at the inputs?
Do you have tranformers lights or LED lights in the room? (Try disconnecting them to see if there is a difference).
Do you have a standard grounding protocal like Star, or Same Length Ground, or Loop Grounding?
Have you measured the voltage and checked Neutral to Ground to see hwat voltage is present? (Try moving power stuff around to see reduce hum.
Are you using Consumer power bars? (These are nasty creatures).
Those are some strating questions.
I chased ground loops my whole life. Never found a perfect answer but usually found a combination of sollutions.
Bruce

[RJH_MUSIC]

Yes, i hear that. NO fun chasing them, and the more gear you have, the more problems arise. I noticed that this went from nice quiet studio to noisy in about 2 months time. I have a separate electrical circuit in the room for all audio gear, so the Computers and lights are all on a different circuit. I do not however have any grounding straps connected to equipment and realize that since I am amplifying an already amplified signal by connecting the BUS outputs of both D8B's to the input channels of a Mackie 32x8 bus mixer, this could amplify the problem. Ha ha forgive the pun..... But problems seemed to appear shortly after the second D8B went down in the early summer when it was extremely hot in the room and we had not turned the AC on in the house yet. I thought the LPS 152 power supply blew again, but it recovered the day after sitting and cooling off. I wonder if it got damaged. But now that i think of it. It is the other D8B that is exhibiting the behavior. I am using balanced audio cables at all the inputs both 1/4" and db25 for the Analog inputs. The only non-constant is back in May I added another 24 channels to the existing 24 inputs utilizing 3 Analog Input cards. The BUS outputs always were a little noisy but now it seems to be on steroids with the added sound that sounds almost at the same pitch as the cooling fans in the d8b. This is another reason i am trying to get a new CPU/PSU built. I thought the Remote CPU might have been too close to the console desks so I moved them recently, but that did not help. I am wondering what components might be getting old inside the console that could cause this. I might try screwing a braided ground wire between the chassis of all three mixers to see what happens. I did notice something odd last night. The led channel meters on the 32x8 bus will periodically flicker one segment when the first d8b (with the noise) without any audio output.

90% of the excess noise is coming from BUS putp0uts 3-4 from the console. Also, running everything at full throttle to diagnose which ones. I wonder if i need a new BUS out cable. Or, maybe i need to pull the console apart one more tie and re-seat cable connectors and clean the analog input jacks on the jack panel.

[Bruce Graham]

Hey RJH_Music;

Yes ground noise is difficult to find. A logical approch is best.

Trying to isolate which device or devices are caussing the noise, I think, is the first step. Once isolated determine if the unit it is noisy on it's own (stand alone, not connected to anything other than power). If clean then add outputs first, one-at-atime, would make sense. Check Audio grounds as you go. As I stated before, I use Output grounds lifted, input ground connected. Once the outputs are connected and clean, then start on the inouts, again one-at-a time.
There are so many other things to check, but I believe the is a right place to start.

There could be an AC Grounding issue as well so remove the ground using a Ground Lift to see if it helps.

Best of luck, Keep us posted as you can.
Bruce

[doktor1360]

Yes ground noise is difficult to find. A logical approch is best.

Trying to isolate which device or devices are caussing the noise, I think, is the first step. Once isolated determine if the unit it is noisy on it's own (stand alone, not connected to anything other than power). If clean then add outputs first, one-at-atime, would make sense. Check Audio grounds as you go. As I stated before, I use Output grounds lifted, input ground connected. Once the outputs are connected and clean, then start on the inouts, again one-at-a time.
There are so many other things to check, but I believe the is a right place to start.

There could be an AC Grounding issue as well so remove the ground using a Ground Lift to see if it helps.

A pragmatic troubleshooting plan of attack, Bruce nailed it. Any issue such as this has to be broken down to the least amount of 'component parts' involved. The manner in which he outlined above is bullet-proof if you follow it thru to the logical ends. It's a 'signal' that's being chased, singular not plural. Start somewhere, and check the input - if more than one input is affected, then follow it back to any previous logic and associated hardware and rinse/repeat until the problem is isolated... until you locate the source of the ground issue you're evidently experiencing. Patience... slow n steady, and you'll find it. It's most likely not gonna go away til you do...

[Standard Mgmt Disclaimer] - "Your actual mileage may vary..."

[RJH_MUSIC]

Well,,,,, there is a point at which I must realize just how stupid I am and fess up with some more enlightening information. I must be getting forgetful in my old age. Ready for a good Laugh?????

So i drove myself crazy for a week now trying to isolate the noise. I brilliantly figured last night that since i have a spare console laying around, i should hook that up to the existing Remote CPU and see what happens. To my delight, 50% of the noise disappeared. While trouble shooting channels I realized that the gain / trim pots were at least 60% turned up on the remaining channels, and when i turned them down, 90% of the noise floated away. So then I took a peak at the trim pots on the console I just replaced and noticed that the majority of them we stationed at approximately 40% - 65% on.... Oh Boy did I feel stupid. Tonight i will put my original console back and turn them down to see what the result is. I bet it will be a lot quieter.. So I am left with sum cycle hum on the Mackie 32x8 Bus which is existent even if nothing is plugged into it. I also noticed that on the 32X8 buss, the left channel buses bleed into the right. If I mute the right side buss, signals on the left channel can be heard on the on the right buss when you raise the left fader. If I mute the left buss, nothing is heard at all on either buss no matter which channel fader is moved up.

[csp]

Not exactly related to the topic, but something that has had me curious ever since I purchased the desk about a year after it was first released. Currently using OS 5.1, Apogee clock card and UFX card

I live in Australia (240Volts) but purchased the desk from a USA (110Volts) dealer.

Being purchased from the USA, like many products, it is only able to be used with 110 volts (I use a 240V - 110V step-down power transformer). Had I purchased the desk in any other part of the world, it apparently came with a change over voltage switch (or possibly a switch mode universal power supply). Why do they make separate units strictly for the USA ???????

Years ago I had a look at the power transformer and on the primary side it has a lead (unused) that has written on the transformer 240V.

At the time, I contacted Mackie in the US and asked if I could remove the 110V connection and wire in the 240V connection and was informed that this was not possible, as it was an entirely different power supply for 240V countries --- sounded very strange to me that Mackie would produce two entirely different power supplies, when a single switch mode supply would have worked !!!

Can anyone advise if what I was told was correct or can I simply swap over the windings and use it directly into the Australian 240V supply. I was always VERY reluctant to do this in case I caused a major problem with the desk.

I did this one time with a pair of active monitor speakers, that I also purchased from the USA (similar situation with the power transformer windings) but set for 110V, however although I connected the marked 240v lead and removed the 110V marked lead, on turning on the speakers it immediately blew the entire amplification circuits on both units and completely wrecked the actual speakers, due to the sudden to power spike and loud audio thump.

If anyone has done this voltage change over from 110 V to 240 V and the desk worked perfectly, I would be most interested to know and was it as simple as changing the two wires.

David

[arjepsen]

Well, you have three power supplies in there. There's the "regular" AT powersupply. Several people have exchanged this for a newer ATX power supply. This supplies power for the motherboard, and also for the 12V line. I don't know if the original one could take both 110 and 240, but as stated, it is possible to do a bit of hacking, and use a newer supply there.

The second supply is the 5V smps. Again, I'm not certain whether this can manage both 110 and 240.

The third on is the +/- 16V linear powersupply, which uses the transformer you mention. Here there is both a question of voltage and amperes. You could try to disconnect the secondaries and measure the output voltages when it's connected to 110V, then (again disconnected from the rest of the circuitry) you could try using the 240V lines, and see if there any big difference in the output voltages. If the voltages are relatively close, it would probably be ok to connect it to the circuitry (no guarantees though...). However, if you want to connect 240 to the general mains input at the AT supply, you need to make sure that both the AT supply AND the SMPS 5V are able to handle that voltage.

Hope I'm not making you more confused.....

[Bruce Graham]

Thanks Dok.
Been chasing Hums and Buzzes all my life at work.
Worst hum I was was a 60 cycle hum that has at 1 volt at the output of my console. Considering the audio signal at +4dbu was 1.4 volts I had little chance of getting the audio over the hum.

Found it after about an hour. There was 85 volts between Ground and Neutral. Shut everything down call the the building electrican who found a faulty ground connection on the water pipe (Building ground. Once fixed ( andf dealt with some other chassis to chassi ground issue between the TV mobile and me, I had gplden silence!

Ground loops and noises can be crazy to find.

RJH, you have a lot of pre amps in your setup, and a lot of console to console, and outboard gear! Chances are you're going to have issues in that setup. Hope you find the rest of it!

Bruce